(1) Field of the Invention
The invention relates to the formation of a self-aligned attenuated rim phase shift mask using exposure of negative photoresist through the backside of a transparent substrate by ultraviolet flood light using a patterned layer of attenuating phase shifting material as a mask. A vertical anisotropic deposition of an opaque layer and a lift off process are used to complete the mask.
(2) Description of the Related Art
The use of phase shift technology in masks used in projection systems to expose a layer of photoresist formed on a semiconductor substrate has become very important as the requirements of image definition and depth of focus have become more stringent. A number of workers have disclosed methods of forming and using phase shifting photomasks.
U.S. Pat. No. 5,358,808 to Nitayama et al. and U.S. Pat. No. 5,376,483 to Rolfson teaches the use of photomasks having a number of phase shifting regions with different optical lengths and different amounts of phase shift.
U.S. Pat. No. 5,403,682 to Lin teaches the use of phase shifting rims surrounding each pattern of a photomask.
U.S. Pat. No. 5,429,897 to Yoshioka et al. teaches the use of attenuating type phase shifting masks.
U.S. Pat. No. 5,393,623 to Kamon teaches the use of reflection type phase shifting photomasks.
U.S. Pat. No. 5,387,485 to Sukegawa et al. teaches the use of photomasks using annular arrangement of light shielding regions together with phase shifting material.
The Invention of this Patent Application teaches the fabrication and use of an attenuating phase shifting rim type photomask. The photomask is formed using self alignment techniques which avoids tolerance build up due to alignment errors.